Transponder Database for Gpredict

Once the new Doppler Tuning Algorithm for Gpredict is implemented and tested, Gpredict needs to have some kind of transponder database to allow easy and convenient selection of transponders for the currently selected satellite.

The idea is to have a data file for each satellite containing one transponder definition per section & or configuration group as it is called in g_key_file terminology. This would also prevent having two transponders for the same satellite having the same name.